Unions in Tableau Semantics

In a logical view, use a union to combine and unify multiple data model objects. You can merge datasets that share similar structures, providing a more holistic analysis of data. Appending ‌values from one object to another results in a comprehensive dataset that integrates information across sources.

Use Case: You have engagement data from different marketing channels stored in separate tables. To get a complete view of how your audience is engaging with your marketing efforts across all these channels, you create a union of these datasets to view all activities, making it easier to see how well your marketing strategy is doing and find trends across your entire plan.

Before you can create a union, you must create a logical view. See Create a Logical View.

• Create a Union
  Merge datasets that share similar structures in a logical view. You can create one union per logical view. You cannot combine unions and joins.
• Delete an Object from a Union
  You can remove an object from the unified table if it is not connected to another object or if it is not being used by another semantic definition. For example, if the object is being used in a calculated field, you cannot remove it from a union. You can also delete the entire union. Removing an object affects the selected matching fields. If only two matching fields exist, removing the DMO eliminates the match entirely, because a single field cannot remain matched.